1. Field of the Invention
This invention relates to improvements in general to semiconductor processing techniques, and more particularly to semiconductor processing techniques that can be used in advanced BiCMOS processes, and in particular to improvements in methods for fabricating high barrier PtSi Schottky diodes in a Ti-Silicided MOS structure which can be used in a high performance BiCMOS processes.
2. Relevant Background
Process techniques have been proposed for the optimal merge of advanced bipolar and advanced CMOS techniques for fabricating BiCMOS devices. Such approaches to advanced BiCMOS processing, however, have been directed primarily to ECL-CMOS applications. Such ECL-CMOS applications do not require the formation of high barrier Schottky diodes, such as PtSi Schottky diodes. The merger of bipolar and CMOS process flows for these applications is therefore relatively straightforward.
Such BiCMOS based approaches generally use TiSi.sub.2 for cladding the MOS gate and its source/drain regions, as well as the emitter, extrinsic base, and collector regions of any bipolar transistors. The process also results in the natural formation of TiSi.sub.2 Schottky diodes. These, however, have a low barrier height of 0.50 V, compared to the 0.90 V for PtSi Schottky diodes. As a result, the TiSi.sub.2 Schottky diodes might not be usable directly in circuit applications.
For those circuits that require high barrier Schottky diodes, such as TTL, STTL and STL logic schemes and also Schottky clamped SRAM cells, a need exists for modifying the Ti-Silicided CMOS-based BiCMOS process so that PtSi Schottky diodes can be easily incorporated in the process. A concern in incorporating PtSi in such a process is the requirement that all processing after the PtSi has been formed be confined to temperatures no higher than 450.degree. C. A further concern in such a process is the presence of TiSi.sub.2 across significant portions of the slice prior to forming PtSi. The present invention discusses several methods for the integration of PtSi Schottky diodes with the minimal addition of processing to advanced BiCMOS processes proposed before in the aforementioned disclosures.